I have the same Bug but I have no SCSI elements and it hangs when I run "/etc/intit.d/networking stop" or restart.
I work with a resolution of 1920x1280 and when it hangs, is quite "curious", all my windows resizes to 1024 (or something like that), unity and app menus dissapear, terminal windows los their focus, some windows can take the focus and you can interact with then but not with the menus.
If I switch off the rj45 cable, then I can't turn the network On until I reboot or shutdown the whole system.

Resolvconf seems to be causing the "hang" in at least one of my testcases. It seems to be attempting to speak with our ldap authentication servers. Strace shows it is trying to lookup the hostnames of the auth servers and the connect to them multiple times for every interface, making the shutdown process take a very long time.

Right, so we appear to have a few things going on here:
- People using networked auth in blocking mode
- People using an iscsi root that for some reason isn't brought up correctly and that ifupdown tries to kill

Those two are likely configuration mistakes as you should never configure a network nss plugin to be blocking, otherwise your boot and shutdown sequence may randomly hang. Instead, there are flags to make the calls immediately return when there's no route available.

Anyone is having this bug and isn't part of one of the scenario above?
If so, please send all the log files asked before and try to explain your setup as best you can.

As the OP, our servers have several interfaces which gives a server access to various subnets. One of these holds the ldap auth servers. If this interface is downed first, resolvconf will hang for ldap.conf TIMEOUT time for every other interface downed. When they're all down (or any default or matching subnet routes), resolvconf/getent passwd returns immediately.

So... In my case, reducing the /etc/ldap.conf /etc/ldap/ldap.conf timeouts or adding a blackhole route with a high metric value matching the ldap subnets would work around this.

As such it can't be categorized as a bug. When I initially chimed in, the problem was masking the infamous scsi kernel softlockup bug.

I'm still puzzled over the nss query resolvconf is triggering. I cannot reproduce it with getent password or similar lookups. For whatever reason resolvconf triggers a query looking for a posixaccount with uid=\2a (uid="*"), which returns 0 results.

Same problem with a ubuntu 12.04.02 on a VM under VMWare ESXi 5.1 with several network interfaces. I also have an LDAP into the network. I've tried by changing the timeout to the ldap but with the same problem.

If I execute the service networking stop; halt it works correctly; the problem is rebooting.

We have been preparing this machine for about a year. It is supposed to work as a a firewall and web proxy connected to about 10 vlans, with DNS server, LAMP, Squid, etc. It's a 64 bit Ubuntu Server perfectly up-to-date.

One week ago we decided it was finished and we moved it into production use. To this point everything was OK. During the last week we configured samba + swat - libpam-smb + cups + hplip and there was a kernel update: on Monday we noticed the hang at the "Deconfiguring network interfaces" but yesterday we saw that it was not a real hang because the system powered off in about tree-four minutes (it used to be about 20-30 seconds).

I have just removed cups + hplip with no success. My next plan is to remove the samba set (I was suspicious of the problems between swat and libpam-smb) and maybe go back to previous kernel as this was the whole story of the last week.

Here, above, I saw some relation between the length of the delay, the point where it happens and the number of interfaces, so I'm writing about it. I may try to add some verbosity, but I have very little clues...

I'm now thinking of going back into this issue. Definitely the problem appeared when installing cups as it requires avahi+mdns packages. This sounds quite fair if cups is to autodetect printers in the LAN.

I've been reading more about mdns. I remember that previously I removed it in certain host to avoid delays in SSH connections and now I have been reading again about it at bug #94940https://bugs.launchpad.net/ubuntu/+source/nss-mdns/+bug/94940. If the delay is caused by mdns it may be amplified when having an interface configured as multiple VLAN sub-interfaces. Cheating nsswitch.conf sounds easier than completely removing avahi+mdns...

So, I would like to know if the rest of the people have avahi+mdns installed and what does their host entry in nsswitch.conf look like. I'm quite confident that keeping "hosts: files dns" as it is now (with avahi+mdns uninstalled) may help in my case.

We also have a MS AD with a .local private domain but I doubt this may interfere as both AD servers switch off every day a couple of minutes before our Ubuntu host does. ¿Do you have .local AD in your LANs?